Chromatin is a DNA and protein complex that forms chromosomes in eukaryotic cells’ nuclei. Nuclear DNA is not found in free strands; instead, it is highly compressed and wrapped around nuclear proteins to fit inside the nucleus.
There are two types of chromatin:
In its expanded form, chromatin appears as beads on a string under the microscope. Nucleosomes are the name for the beads. In each nucleosome, DNA is wrapped around eight proteins called histones. Additional histone proteins support the chromatin structure by wrapping the nucleosomes into a 30 nm spiral called a solenoid. The structure of chromatin and chromosomes can be seen under a light microscope during cell division, and they change shape as the DNA is duplicated and separated into two cells.
Chromatin is a DNA-protein complex found in eukaryotic cells. Long DNA molecules are compressed and densified into smaller, more compact structures.
This keeps the strands from getting tangled, as well as reinforcing the DNA during cell division, preventing DNA damage, and controlling gene expression and DNA replication.
In anaphase during mitosis and meiosis, chromatin aids proper chromosome segregation; the distinct shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed chromatin.
Histones, which bind to DNA and serve as “anchors” around which the strands are wound, are the most important protein components of chromatin.
There are three levels of chromatin organization in general:
Many organisms, on the other hand, do not adhere to this organizational scheme. Most eukaryotic cells, for example, have more tightly packed chromatin than spermatozoa and avian red blood cells, and trypanosomatid protozoa do not condense their chromatin into visible chromosomes at all.
Prokaryotic cells have completely different DNA organization structures than eukaryotic cells.
The overall structure of the chromatin network is also affected by the cell cycle stage. The chromatin is structurally loose during interphase to allow RNA and DNA polymerases to transcribe and replicate the DNA.
The specific genes present in the DNA determine the local structure of chromatin during interphase. In a structure known as euchromatin, regions of DNA containing actively transcribed genes (“turned on”) are less tightly compacted and closely associated with RNA polymerases, Inactive genes (“turned off”) are generally more condensed and associated with structural proteins, whereas regions containing inactive genes (“turned off”) are generally more condensed and associated with structural proteins.
Epigenetic methylation and acetylation of chromatin structural proteins affects local chromatin structure and, as a result, gene expression.
The process of packaging DNA into nucleosomes is the simplest definition of chromatin assembly. Histone chaperones and ATP-utilizing factors catalyze the deposition of histones on DNA to produce periodic arrays of nucleosomes, which is the basic chromatin assembly process.
Histones package DNA into chromatin. Chromosomes are formed when chromatin is condensed and organized further. Chromatin is not paired like chromosomes.
Inside the nucleus of eukaryotic cells, chromatin is a complex of macromolecules made up of DNA, RNA, and protein.